Method and apparatus for translating sound



Feb. 16, 1932. w. RICHMOND METHOD AND APPARATUS FOR TRANSLATING SOUND Filed March 12, 1920 2 Sheets-Sheet l Feb. 16, 1932. w, RlCHMOND 1,845,986

METHOD AND APPARATUS FOR TRANSLATING SOUND Filed March 12, 1920 2 Sheets-Sheet 2 F1545 1M flaw M gwoentoz Patented Feb. 16, 1932 RICHMOND, OF GLEN ELLYN, ILLINOIS METHOD AND AHIEARATUS FOR TBANSLATING SOUND Application filed March 12, 1920. Serial No. 865,820.

This invention relates to a method and apparatus for translating sound. Heretofore in the translation difficulties have been experi enced in recording and reproducing sound waves clearly.

These various difiiculties, their causes and efl'ects, and the manner in which I have overcome them and made possible true and clear recordation and reproduction of sound of controlled volume will become apparent from the following specification.

One object of my invention is to eliminate vibrations of various parts of the recording or reproducing apparatus, record and reproduce the original sound waves clearly andto reduce distortion or interference of other waves.

Ill

Another object of my invention is vto reproduce the original sound waves and at the same time eliminate other sound waves which from various causes inherent in many pres? ent reproducers find their way into the amplifying devices of commercial talking ma- Another object of my invention is the substantial translation of sound waves into their equivalent mechanical or electrical waves or the reverse, the translationof mechanical or electrical waves substantially into their equivalent sound waves without a noticea'ble addition or introduction of interfering waves.

Another object of my invention is to pro 'duce a diaphragm so delicately poised that it will respond to very slight variations in tone or magnitude of vibration and at the same time so constructed and actuated that it can swing through a greater amplitude than the greatest amplitude of vibration to which it will be subjected in use, thus enabling the reproduction of sound waves of greater vol ume than the original waves free from 'noticeable distortion in tone or clearness.

Another object of my invention is 21. diaphragm which will not lag appreciably behind the impressed vibration but will reach the limit of its greatest vibration substantially in unison with the impressed vibration and which will return to its normal position as rapidly'as the cycle of the particular tone which is being impressed.

Another object of my invention is a diaphragm, difierent portion of which have difierent periods of vibration or different key notes.

Another object of my invention is adiaphragm which, as a whole, has no key note.

Another object of my invention is to obtain clear enunciation in the reproduction of sound waves.

Another object of my invention is to improve the reproduction of the human voice and to reduce the metallic, mechanical sounds such as are produced by many commonly used translating devices.

Another object of my invention is to record and reproduce sound waves so that they have substantially the same volume as the original sound waves without seriously impairing the quality of tone or enunciation as distinguished from various expediencies which have been in use, such as the fibre needle which produces fairly good tones but of such small volume as to be undesirable.

Other objects and advantages of other features of my invention are more fully set forth in the applications Serial Numbers 500,660; filed December 6,- 1930, and 500,661, filed December 6, 1930, both of which applications are divisions of this application.

. In the drawings: Fig. 1 isa .side elevation of a form of reproduce! embodying the principles of my invention, part thereof being shown with the casing removed for purposes of clearness.

Fig. 2 is a bottom plan view of thereproducer illustrated in Fig. 1.

'Fig; 3 is a somewhat diagrammatic illustration of one'of the arrangements of magnets and electric circuits which may be used in my invention.

Fig. 4 is a reduced view of the right half of the reproducer, as illustrated in Fig. 2,

vvhich the reproducer may-be attached.

and is taken on a plane indicated by the line CC of Fig. 2.

Fig. 5 is a reduced view of the left half of the reproducer as illustrated in Fig. 1, and is taken on a plane indicated by the line BB of Fig. 1.

Fig. 6 is a side elevation of the body member of the reproducer illustrated in Figs. 1 and 2 illustrating the mounting of the stylus bar thereon and the rubber spacing ring and diaphragm. V

Fig. 7 is a detail plan View of one form of torsion spring suitable for use in'my invention.

Fig. 8 is a side elevation of the clamping ring of the reproducer illustrated showing another means for mounting the torsion spring.

Fig. 9 is a plan view of a diaphragm suitable for use in my reproducer.

Figs. 1011 and 12 are cross sectional views illustrating forms of diaphragms which may be used in connection With my invention.

Fig. 13 is a cross-sectional view of a diaphragm similar to that illustrated in Fig. 9 and is taken on a plane through the center thereof.

Fig. 14 is a cross-sectional view of a preferred form of throat for use in my reproducer and is taken on a plane indicated by the line A-A of Fig. 5.

Referring to the drawings, Fig. 1 illustrates an embodiment of my invention in a reproducer having a body member 1 or principal part to which other parts are attached.

This body portion may be of either metal or Wood and is preferably in the form of a disk having a central opening in which is mounted the sound tube 2 for the transmission of sound waves to any amplifying device. to ;\S illustrated in Figs. 1 and 2, a diaphragm 3 is mounted on the body 1 by a clamping ring 4, the diaphragm being spaced from the body 1 by a rubber ring 5. This assemblage may be conveniently made by clamping the ring 4 against the body 1 by means of screws such as 6 and 7. In the form illustrated, the sound tube 2 passes through the body, 1 and terminates in the plane of the face of the body 1 adjacent to the diaphragm. Forpurposes of clearness the sound shown in Figure 2.

The ring 5 is preferably removable and tube 2 is not may be made of rubber or other suitable material. This ring is placed between the diaphragm 3 and the face of the body 1 to space ance from the the opening of face of the body 1 and from the sound tube 2. The ring 5. however, ma i be formed integral with the body 1 and of a predetermined thickness so as to definitely fix the distance between the face of the diaphragm 3 and the adjacent face of the body 1 or the opening in th sound tube The asaaese clamping ring 4 may be recessed, as better shown by the dotted line 8 in Fig. 8 to accommodate both the diaphragm and the rubber ring 5. The clamping ring t is slotted to form a passage for the stylus bar 13 when the stylus bar is mounted in one or" the ways later to be described.

Screwed, or otherwise rigidly :tastenedto the body 1 is a supporting plate 9 to which the endsof a torsion spring 10 are secured.

However, if desired, instead of using the plate 9 suitably spaced lugs 11 may be cast or fastened on to the clamping ring 4 as lllustrated in Fig. 8.

The torsion spring, the purposes of which will now be described, may comprise a thin piece of metal. For example steel of 20/1000 of an inch thickness may be used.

In the present types of sound reproducers and recorders in which the stylus bar is actuated by a record, the stylus bar is usually mounted on pivots and has no tendency to return to its normal position after it has been actuated. Therefore it will lag appreciably behind the vibrations inpressed upon it and return to its normal position only as a result of its being moved by the record or the diagram. lVhen the diaphragm is so hampered it will not produce a true tone or faithful reproduction but a distorted wave. To eliminate this undesirable action I actuate my stylus bar with a torsion spring.

The end portions only of the torsion spring engage the plate 9 orthe lugs 11, these end portions being provided with screw holes for fastening the torsion spring onto the plate 9. The stylus bar is rigidly secured to the spring, preferably at the center thereof, and extends to the center of the diaphragm. A suitable means of connecting the stylus bar to the spring is by means of a lug 12 rigidly secured to the stylus bar. This lug may project laterally and be provided with a bore to receive a stylus and a thumb screw to retain the stylus therein. As one example, a torsion spring of less width than its end or supporting portions may be used the spring having a small central enlargement so that the stylus bar or lug supporting the same may be conveniently fastened thereto by screws. This type of spring is illustrated in Fig. 7. A stylus bar so mounted can vibrate by twisting the narrow portions of the torsion spring. For instance, in the case of reproduction of sound from lateral cut records the sound grooves of the record are lateral of the path of movement and the record transmits a lateral movement through the stylus to the sty lus bar by twisting the stylus bar about the i-x i tudinal torsional axis of the torsion spring. The width of the spring in the direction of motion of the stylus is sufiiciently great to prevent any latera the support of 1 the stylus bar, so that the spring allows only a torsional or twisting movement similar to the movement which the stylus bar would have if it were mounted on pivots. At the same time, the stylus bar is returned to its.

normal position by the torsion spring no matter in what direction it has been moved or twisted by the action of the recordon the stylus This return is rapid, the vibrating period or cycle of the stylus bar and spring being in direct proportion to the breadth and thickness and inversely proportionally to the length of the torsion spring. I make the torsion spring relatively short and thick, using for instance, steel 20/1000 of an inch in thickness. Such a spring is of such high pitch that it does not have any tendency to blur or distort the sound waves transmitted through the stylus bar to the center of the diaphragm. Further, it raises the pitch of the stylus bar 13 and actuates it while keeping the pitch of the stylus bar higher than that of the human register. Therefore the stylus bar has no tendency to swin in unison with, or to impress its own perio of vibration on the vibrations received from the record.

Another point at which sound waves are distorted in many talking machines is at the center of the diaphragm where there is a combination of a. slow moving diaphragm and a slow moving stylus bar which must be overcome by the power transmitted from the record. The torsion spring described is of sufficient strength to actuate the diaphragm also. Thus the key note of the entire assemblage as well as each part is raised above the audible range. This gives the stylus bar and the assemblage a period of vibration or key note which is out of the audible range of vibration and consequently the combined diaphragm, stylus bar and spring do not synchronize with impressed vibrations and have no tendency to swing in unison with them or to impress their own period of vibration on them. ;Obviously, the same is true of the torsion spring itself. Therefore, vibrations which are carried up the stylus bar to the diaphragm are substantially free from chatter. and any tendency of the stylus bar or the torsion spring to vibrate in unison with impressed vibrations and transfer the resultant vibrations to the diaphragm so as to blur the sound reproduction or recordation is eliminated. Such vibrations as are impressed upon it to cause it to vibrate in unison therewith will be only such sounds as will not affect the human ear, as they will be above the audible range. Since the stylus bar and diaphragm thus are actuated and are raised in pitch by a torsion spring of such a high period that they will not appreciably distort the impressed vibrations, I can employ a magnetically sensitive diaphragm that is, a diaphragm which is composed of or includes a soft metal and which diaphragm has practically no period of vibration of its own.

In some cases, however, I prefer to use a diaphragm of spring tempered steel or other spring tempered material, preferably in the form of a disk mounted as a diaphragm in the diaphragm ring of the reproducer. In such cases, due to the fact that the diaphragm has a spring action and will return to its normal position almost as rapidly as it is moved by theilnpressed vibrations the stylus bar when employed may be mounted on pivots in the usual fashion and without a torsion spring.

For instance, the spring tempered diaphragm in Fig. 13 has its own tendency to return to normal position and to return the stylus bar and hold the stylus bar at a higher pitch than the ordinary diaphragm would do and consequently, the stylus bar may be mounted on pivots, as stated.

As set forth in the objects of my invention, it is necessar to have a diaphragm so delicately poised t at it will respond to very slight variations in tone or magnitude of vibration and, at the same time, of such resiliency that it can swing through a eater amplitude than the greatest amplitudd of vibration that will be impressed upon it when in use. When I speak of a resilient diaphragm, I mean one which will reach the limit of its greatest vibration substantially in unison with the impressed vibration and which will return to its normal position as rapidly as the cycle of the particular tone which is being impressed. In other words, the diaphragm must not lag appreciably behind the impressed vibrations or there will be what is known as distortion. This distortion, in reality resultants of the diaphragm tone caused by its lagging behind the impressed vibration, is overcome by the torsion spring, my magneto electric circuit, later to be described, and a diaphragm having no keynote as a whole but having a period of vibration below the audible range.

I have found that many diaphragms of a single substance have a fixed period of vibration or a key note to which they will respond more readily than they will to any other period of vibration. Further, I have found that a velvety softness can be imparted to the sound waves leaving a diaphragm by having the'working side of the diaphragm present a soft fibrous surface, blotting paper serving as a fairly good illustration of such soft fibrous surface. For example, a hard fibre diaphragm one face of which is covered with blotting paper may be used. In the case of reproduction of the human voice, for example such a soft fibrous working surface on a diaphragm will give to the sound waves leaving the diaphragm a more natural human tone. Also it will give an improved tone to the sound wave of whatever instrument is being reproduced.

Further, I have found that if a diaphragm is divided into two or more diaphragms or portions. by the use of a smaller diaphragm or by rings riveted, or otherwise secured in place on the diaphragm, each of the portions will have a period of vibration of its own and thediaphragm will be in effect, a compound diaphragm having a keynote as a whole. 1

I shall now discuss a number of diaphragms embodying the principles above enumerated.

The diaphragm illustrated in Figs. 9 and 10 has been divided into two or more diaphragms or areas by use of aring or annulus 14 secured in place on the diaphragm by rivets 15 or otherwise. This ring, or rings, if more than one is used, may be of the, same material as the diaphragm or of astifi'er material. A diaphragm with rings so mounted will have-portions each having a difi'erentperiod of vibration. From observation it ap pears that the outer diaphragm or portion 16 will have a low ring section or. annu us 14 will have a higher period of vibration and the inner diaphragm or central circular portion 17 will have a still higher period of vibration. Each area responds to difi'erent periods of vibration and each area will respond more readily to its own key note. For this reason the diaphragm as illustrated has no key note to which it will respond as a whole, 7

T have found that a diaphragm divided into three diaphragms or portions as illustrated in Fig. 9 gives very desirable results in the separation of sounds of difi'erent pitches. As a concrete example the co-mingling vibrations resulting from the voice waves of a quartet traveling up the stylus bar to the center of such a diaphragm appear to be. separated and each voice brought out clear and distinct and separate from the other voices, the outer diaphragm being responsive to the voices in the lower register, and the middle diaphragm being responsive to the voices in the middle register and the inner diaphragm being responsive to the voices in the higherregisterg Thus desired and distinct separation of different voice tones and difierent toned instruments or of a plurality of sounds having different wave lengths is obtained. By the use of such a diaphragm, I have been able to distinguish two voices singing in harmony. 1

To use this type of diaphragm efiectively in mymagneto electric reproducer it is only necessary that the ring it be magnetically sensitive. The material which I use for the diaphragm in such case may either be magnetic or non-magnetic. in fact any material commonly used for diaphragms is satisfactory.

These rings will be operated on by the magneto and electric members of my reproduccr eriod of vibration, the.

neaaese and will give substantially the same results as though I had used a completely magnetic or magnetically sensitive dlaphragm.

This type of diaphragm may be covered on one side by a soft fibrous material as above mentioned. This fibrous surface imparts to either magnetic or non-magnetic as stated.

In Fig. 11 is illustrated a diaphragm, composed of two or more substances. For instance, the diaphragm may be composed of a material either magnetic or non-magnetic and a soft fibrous material -l8 or of a hard fibrous material with a soft fibrous material or of mica and a soft fibrous material, an ob- 'ject being to secure a resilient diaphragm with a soft and roughened fibrous surface which produces better tones than the harsher or metallic side of the diaphragm.

Fig. 12 illustrates a diaphragm divided into three diaphragms or portions, each having its own key note and in addition has the advantages of a diaphragm composed of two or more substances as illustrated in Fig. 11. As stated, the outer portion appears to vibrate more in unison w1tl1 the lower tones, the super-imposed rings 19 in unison with tones of the middle register and the small inner portion responding more readilyto tone of the upper register,for example,the soprano. The soft fibrous covering producesbetter and more natural tones in all registers and thus renders the diaphragm especially effective for reproducing the human voice clearly. In such a diaphragm the d sired and distinct separation of the voice tones of difierent pitches are obtained and slurring and blurring are eliminated. This soft fibrous surface is designated at 20.

Another type of diaphragm is illustrated in Fig. 13. This diaphragm is a compound diaphragm composed of spring tempered steel or other spring tempered disk 21 divided into three parts by a ring or rings 22 soldered or otherwise fastened in place on the diaphragm for the purpose described. The whole diaphragm is covered with a thin. layer of soft fibrous material 2%. The action of this diaphragm is similar to the one illustrated in Figs. 9 and 12 with the exception thatit is resilient within itself and has its own tendency to return to its normal position consequently it may be used in a reproducer the stylus bar of which is mounted on pivots as previousl described and thus dispense with the use 0 a spring or resilient mounting for the stylus bar.

In the drawings of the diaphragm the thickness of the diaphragm and of the rings 'has been exaggerated for clearness in illustration.

Referring now to the magnetic elements of my invention, one action of permanent magnets on the diaphragm is to eliminate dia phragm noises. Any diaphragm susceptible to magnetic action will, when vibrating from extraneous causes, in a magnetic field, become what is usually known as dead beat, that is, it will lose its tendency to vibrate in its own key note and will tend to come instantly to rest in unison with the cessation of vibrations imparted to it by a stylus bar, or otherwise. An action of the electric winding is to reduce the power required to set the diaphragm in motion against the resistance of the magnets without detracting from the ability of the permanent magnets to render the diaphragm dead beat. Thus the diaphragm may be started and vibrated freely from its normal position of rest and consequently increasing the amplitude of vibration of the diaphragm and amplifying the emitted sound without causing distortion or interfering tones is rendered possible.

I will now describe one arrangement of magnets and windings which I have found eflective.

Mounted on and forming part of the face of the body 1 are permanent magnets 24 and 25. These permanent magnets extend through the body 1 to its face, as illustrated, the pole faces of the magnets forming part of the face of the body 1 i. e., lie in the plane of the face of the body 1 adjacent to the diaphragm as shown in Fig. 1. In the reproducer or recorder illustrated in Fig. 1 these permanent ma nets are held rigidly in lace on the body 1 by a non-magnetic metal ox 26 which is screwed, or otherwise fastened, to the body 1. This box 26 also holds the outer end of the sound tube 2 rigidly in place. The permanent magnets 24 and 25 are firmly clamped against two ends of the box 26 by the pieces 27 and 28, the screws passing through the center of these pieces as shown at 29 in Figs. 1 and 2 and between the two prongs of the'permanent magnets and into the box 26. Electric windings 30 and 31 are provided on the poles of the permanent magnets 24 and 25. One of the windings which I have used is diagrammatically shown in Fig. 3. The windings comprising eight coils in all when magnets are used on both sides of the diaphragm, may be connected in series, series multiple or multiple or each coil may be short circuited, depending on the quality of the tone and their particular actionon the various types of diaphragms that may be used.

If all the windin s on one set of magnets on one side of the iaphra-gm are connected in a closed circuit with each other, a very heavy opposing flux could be obtained which would be effective when the diaphragm swings toward such magnets. This flux would very abruptly arrest vibration of the diaphragm when it passed a given point in its path of movement. On the other hand, the coils at one side of the diaphragm may be connected with the coils at the other side in such manner that the flux toward which the diaphragm moves induces a current in the windings which is transferred to the other side of the diaphragm and may either assist movement of the diaphragm or may oppose movement depending upon which termini of the opposite coils are connected. Other noticeable effects can be obtained by different combinations of these windings, especially when coils on opposite sides of the diaphragm are connected together. A few trials will demonstrate the particular windings and connections desirable for the diaphragm that is being used. With a non-metallic diaphragm carrying a metal annulus, I obtained the best results by connecting the coils on one side in series multiple with the coils on the opposite side.

The opposite magnetic assembly composed of permanent magnets 32 and 33, the spacing block 34 and the clamping members 35 and 36 together with the electric windings on the poles of the permanent magnets 32 and 33 are held with the pole faces of the magnets in spaced relation to the diaphra m by the supports 37 and 38 shown in ig. 2. These supports 37 and 38 are soldered or otherwise fastened to the clamping members 35 and 36 as shown in Fi 2 and are rigidly secured to the body mem er 1 by the screws 39 and 40. A portion of the support 37 is shown in Fig. l with its two fastening screws. A portion only is shown, the remainder being cut away to show the magnetic members more clearly. I have already described the various connections for the electric windings on permanent magnets. As described, permanent magnets are used on opposite sides of my magnetic diaphragm which may be composed of magnetic material or a metal which, when it is vibrating in a ma etic field, will in effect be a short circuite electric conductor around the lines of force and in effect become magnetized and act and react with the electric windings on the poles of the permanent magnets. I have secured some good results usin .aluminum, copper and brass diaphragms or this induced electromagnetic effect.

The pole faces of the premanent magnets on opposite sides of the diaphragm are of opposed polarity. The electric and magnetic members of this invention are in no sense of the word electromagnetic and use no battery or outside power for their operation. Electromagnets could be used but would require the vibrations which come up the stylus bar to be translated into clear, concise, tones without wave interference from the diaphragm. There are a large number of arrangements of connections between the coils of opposed magnets and between the coils of each set of magnets, each of these varying connections giving a different result. As additional examples, all or part of the windings of the magnets on one side of the diaphragm may be connected in series, series parallel or multiple with those of the other side or with each other, or short circuited. For these reasons, my reproducer could be put on the market to accomplish definite and different results.

It will be understood that I can make this invention in a more compact form by using ring magnets, with soft iron pole pieces projecting toward the diaphragm at the proper points and carrying the electric windings. Other obvious methods of making the reproducer in a compact form may be used without departing from the spirit of the invention.

For use with diaphragms which do not secure perfect separation and enunciation, I have provided a throat and orifice. The throat 41 is shown in Fig. 14.- in cross section. The orifice 42 is shown only in Fig. 5 and is located within the sound tube 2. The throat is perferably made of cork although it will give desirable results if made of metal. I

have discovered that the peculiar shape of the throat and orifice as shown at 42, Fig. 14, tends to produce clearer tones in almost any of the present types of talking machines. In the case of human voice, for example, a greater clarity in enunciation is discernible when the orifice is used.

The outer end of the sound tube 2 is a slipon connection for fastening the reproducer to the tone arm of a talking machine. There are numerous elbows now on the market which if interposed between the outer end of v the sound tube 2 and the tone arm of a talk- By the use of these generic features the translation of sound waves substantially into their equivalent mechanical or electrical waves or the reverse, the translation of mechanical or electrical waves into their equivalent sound waves, is accomplished without noticeable addition or introduction of interfering waves, or more broadly the translation of one class of waves into waves of another class and the retranslations from this class into the original class of wave is accomplished without the final wave having suffered any noticeable deterioration from its several translations.

Various changes in the details of construction and arrangement of parts may be made without departing from the spirit of my invention or the scope of the appended claims.

Having thus described my invention, I claim:

1. A diaphragm and means dividing said diaphragm into a plurality of clearly defined substantially concentric annular portions and a closed circular central portion, the radial widths of each of said annular portions being less than the radius of the central portion and each of said portions having a different key note within the audible range.

'2. A diaphragm and means dividing said diaphragm into a plurality of clearly defined portions, each of said portions having a key note or natural period of vibration within the audible range and different from the nat ural period of vibration of each of the other portions, said diaphragm being comprised of layers of different materials.

3. A thin metallic diaphragm having a thickened annular portion dividing the diaphragm into a plurality of substantially concentric portions, each of said portions having a different period of vibration, said annular portion being intermediate the periphery and center of the diaphragm and spaced therefrom.

4. A thin metallic diaphragm, a metallic annulussecured on said diaphragm and dividing said diaphragm into a plurality of substantially concentric annular portions, each portion having a different degree of stiffness.

5. A metal diaphragm, a plurality of stiff annnli on said diaphragm dividing said diaphragm into substantially concentric areas,

said annulil 'ng intermediate the center and periphery 0 the diaphragm.

6. A metal diaphragm, an annulus carried on said diaphragm and a soft fibrous material covering one face of said diaphragm and fpresenting the fibres of its outer face in a so pliant condition.

7. As a unitary structure, a thin metallic diaphragm having a stiffened annularportion dividing the diaphragm into a plurality of concentric portions, a soft fibrous material covering the outer face of at least a centrally of different de disposed one of said concentric portions, said the soft fibrous material, all of said members 1 being secured together to form a unitary structure and the fibrous material presenting the fibres of its outer face in a soft, pliant condition.

9. A metallic. diaphragm and a soft fibrous material covering one face of said diaphragm and forming therewith a unitary structure, said fibrous material presenting the fibres of its outwardly disposed surface in a' soft, pliant condition.

10. A diaphragm and means dividing said diaphragm into a plurality of substantially concentric annular portions, each of said portions having a key note or natural period of vibration within the audible range and different from the natural period of vibration of each of the other portions, one face of said diaphragm being covered with soft, fibrous .material, said material presentin the fibres of its outer surface in a soft, pliant condition.

11. A diaphragm of resilent material and soft fibrous material covering one face thereof and secured thereto and forming therewith a unitary structure, the said fibrous material presenting the fibres on its outer face in a soft, pliant condition.

12. A diaphragm, and means on said diaphragm stifienin an annular rtion of said dia hragman dividing said iaphragm into su tantiall conoentrlo annular rtions, said dia being compose of spring temper metal.

the other portions, said diaphragm being composed of spring tem red metal.

14. A diaphragm 0 spring tempered metal including aluminum, and means divid-' ing said diaphragm into a plurality of sub stantially concentric annular portions and a central circular portion, said portions being es of stiffness; f

15. A dia ragm of spring metal, said stifl'ened portion dividing sai jdiaphragm into a plurality of clearly defined substantially concentric portions.

16. A diaphragm of spring tempered metal, a soft fibrous material covering one face thereof and forming therewith a unitary structure, said fibrous material presenting the fibres of its outer face in a soft,-pliant condition.

iaphragm havin an annular" 17. A diaphragm and means dividing said diaphragm into a plurality of clearly defined substantially concentric annular portions and a closed circular central portion, the radial widths of one of Said annular portions being less than the radius of the central portion and each of said portions having a different key note within the audible range.

18. A diaphragm formed of stiff material and having a period of vibration out of the audible range.

19. A composite diaphragm having a natural period of. vibration out of the audible range.

20. A composite diaphragm having a. natural period of vibration out of the audible range, in which each portion com osing the diaphragm has a. natural period 0 vibration within the audible range.

21. A diaphragm having a period of vibration above the audible range.

' 22. A diaphragm having a period of vibration below the audible range.

23'. .A diaphragm of spring tempered material, said diaphragm having an annular stiffened portion dividing the diaphragm into a plurality of portions having a natural period of vibration within the audible range, said diaphragm as a whole having a period of vibration out of the audible range.

24. A diaphragm assembly having a period of vibration out of the audible ran e.

WALTER RICHMONd).

cerxrirrea're er eennnacrien.

Patent No. 1,845,986. Granted February 16, 1932, to

Warren intentions.

it is hereby certified that error appears in the printed specification of the aheve nnrnhered patent requiring eorreetien es ioilows: "Page 1, line 3, after the word "translation" insert the words oi soend wnves, and iine 27, for "on" read one; page 2, line 75, after "seenred. insert the ioilowing sentence "intermediete the points of connection of the spring to the plate, the plate is reeessed, as illustrated, the spring bridging this recess"; line 90, ior "inpress ed" read impressed, and line 93, for "diagram" read diaphragm; page 4, line 10, ior the article "a" first occurrence read no, and line 105, ior "tone" read tones; page 5, line 126, for the misspelled Word "premanent" read permanent; and that the said Letters Patent should he read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and seated this 22nd day of March, A. D. i932.

M. J. Moore, ($eai) Acting Goissioner of Patents. 

